Optical deflector and method of producing same

ABSTRACT

There are provided a small optical deflector that can be driven at a high speed with a low voltage, provides a large angle of deflection, has a low distortion even in high speed operation and has a high static flatness of a reflective surface, and a method of producing the optical deflector. The optical deflector drives a movable plate relative to a supporting substrate to deflect a light incident on a reflective surface and has a configuration in which at least two recesses are formed in a surface of the movable plate on which the reflective surface is not formed, and a magnetic material is provided in the recesses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical deflector that deflectsincident light, a method of producing the same, and an optical deviceusing the same.

2. Related Background Art

In recent years, with the development of microelectronics as representedby the increasing integration density of semiconductor devices, variousdevices have been enhanced in capability and reduced in size. Forexample, image display devices, such as laser beam printers andhead-mounted displays, and optical intake units or the like of inputdevices, such as barcode readers, in which an optical deflector is usedfor optical scanning, have also been enhanced in capability and reducedin size and are being required to be further down-sized. Opticaldeflectors meeting such a requirement have been proposed in JapanesePatent Application Laid-Open No. 6-82711 (no corresponding document inforeign language) and Japanese Patent Application Laid-Open No.2000-147419 (no corresponding document in foreign language), forexample.

FIG. 16 is a perspective view of a first conventional optical deflectordisclosed in Japanese Patent Application Laid-Open No. 6-82711.

A scanning mirror 1001 of the optical deflector is in the form of arectangular plate and comprises a glass plate 1009, a mirror part 1002capable of reflecting a light formed on one side of the glass plate byevaporation of aluminum or the like, and a rare-earth permanent magnet1003, such as a samarium-cobalt (SmCo) magnet, formed in the shape of athin film on the other side of the glass plate by sputtering or thelike. Supporting members 1004 in the form of strips made of a metal, forexample stainless steel or beryllium copper, are each fixed, at one endthereof, to the center of both longitudinal ends of the mirror part 1002and supported thereon and fixed, at the other end thereof, to a devicemain body (not shown). The angle of the scanning mirror 1001 can bechanged around a torsion axis 1005 connecting the supporting members1004 by torsion of the supporting members 1004. The permanent magnet1003 is magnetized so as to have opposite polarities on both sides ofthe driving axis 1005, as shown in FIG. 16.

Furthermore, a magnetism-generating unit 1006 comprises a coil frame1008 and a coil 1007 wound around the coil frame and is disposed at apredetermined distance from the side of the scanning mirror 1001 onwhich the permanent magnet 1003 is formed. Therefore, when the coil 1007is energized, the magnetism generating unit 1006 generates magnetism,and an attractive or repulsive force arises between the magnetic polesof the permanent magnet 1003 and the magnetism generating unit. Theforce activates the scanning mirror 1001 and displaces the same to anyangle according to the magnetism generated by the magnetism generatingunit 1006.

FIG. 17A is an exploded perspective view of a second conventionaloptical deflector disclosed in Japanese Patent Application Laid-Open No.2000-147419, and FIG. 17B is a schematic sectional view taken in thelongitudinal direction of the optical deflector of FIG. 17A.

As shown in FIG. 17A, an optical deflector 2001 has a planar rectangularbase 2002. A ridge 2003, formed integrally with the base 2002, protrudesfrom the entire outer periphery of the base 2002, and a vibration unit2005 is provided on the ridge 2003.

The vibration unit 2005 comprises a rectangular outer frame 2006, areflective mirror 2007 having a reflective surface 2007 a formed thereonand disposed in an opening 2006 a of the outer frame 2006, and a pair ofsupporting parts 2008 that couples the reflective mirror 2007 and theouter frame 2006 with each other along an axis substantially passingthrough the center of gravity of the reflective mirror 2007. The outerframe 2006 is fixed to the ridge 2003, and the reflective mirror 2007can be swung around the pair of supporting member 2008 serving as atorsion axis CL.

On the back surface of the reflective mirror 2007, there is formed amirror-side comb section 2009 composed of a groove 2009 a and aprojection 2009 b extending in a direction perpendicular to the torsionaxis CL. A pair of fixed electrodes 2010 and 2011 is disposed on thebase 2002 so as to be in opposition to the mirror-side comb section 2009of the reflective mirror 2007, and also on the upper side of each of thepaired fixed electrodes 2010 and 2011, there is formed an electrode-sidecomb section 2012 composed of a groove 2012 a and a projection 2012 b.The mirror-side comb section 2009 and the electrode-side comb section2012 are disposed in such a manner that the groove 2009 a and theprojection 2009 b engages with the groove 2012 a and the projection 2012b. Further, as shown in FIG. 17B, between the fixed electrodes 2010,2011 and the reflective mirror 2007, a voltage can be appliedselectively via switches SW1, SW2, respectively. Therefore, alternatelyturning on and off the switches SW1 and SW2 to alternately apply avoltage to the paired fixed electrodes 2010, 2011 can swing thereflective mirror 2007 around the torsion axis CL corresponding with thepaired supporting members 2008.

However, these first and second conventional examples have problemsdescribed below.

In the first conventional example, to activate the mirror part 1002 at ahigh speed and with a large angle of deflection, it is desirable thatthe moment of inertia of the scanning mirror 1001 around the torsionaxis 1005 is small. A possible approach for reducing the moment ofinertia of the scanning mirror 1001 in the arrangement according to thefirst conventional example is to reduce the thickness of the supportingmembers 1004. However, if the thickness of the supporting members isreduced, the rigidity thereof is also reduced. Therefore, when thescanning mirror 1001 is activated to torsionally vibrate at a highspeed, the scanning mirror 1001 significantly fluctuates in positionbecause of the inertial force caused by the self-weight thereof. Thus,there is a problem that it is difficult to provide both of action of thescanning mirror at a high speed and with a large angle of deflection andoptical characteristics of the optical deflector.

In addition, if a high magnetism generating power is required, thethickness of the permanent magnet 1003 has to be increased. Thus, thereis another problem that the moment of inertia of the scanning mirror1001 significantly increases, and the center of gravity of the scanningmirror 1001 is largely displaced from the torsion axis 1005 and a stabletorsional vibration cannot be attained.

In the second conventional example, to activate the reflective mirror2007 with a large angle of deflection, the projection 2009 b of themirror-side comb section and the electrode-side comb section 2012 arerequired to have a sufficient height in order to avoid interferencebetween the reflective mirror 2007 and the base 2002. Thus, there is aproblem that the moment of inertia of the reflective mirror 2007inevitably increases as the angle of deflection increases, and it isdifficult to provide both driving characteristics of high speed and alarge angle of deflection.

In addition, in the second conventional example, since an electrostaticactuator requires a higher voltage than an electromagnetic actuator, thepower supply unit inevitably has a large size. Thus, there is a problemthat, even if the optical deflector can be reduced in size, the drivingunit still has a large size, and the size of the whole device is stilllarge.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the problems of priorart described above.

It is, therefore, an object of the present invention to provide anoptical deflector that can be driven at a high speed with a low voltage,provides a large angle of deflection and a low distortion even in highspeed operation, and has a high static flatness of a reflective surfaceand a small size. Another object of the present invention is, a methodof producing the optical deflector and an optical device using theoptical deflector.

According to a first aspect of the present invention, there is providedan optical deflector, comprising:

-   -   a supporting substrate having an elastic supporting part;    -   a movable plate having a reflective surface on one side thereof        and a magnetic material on another side thereof and supported at        both ends thereof by the elastic supporting part so as to be        torsionally vibratable around a torsion axis; and    -   magnetism generating means provided in the vicinity of and        spaced apart from the magnetic material, for driving the movable        plate relative to the supporting substrate to deflect a light        incident on the reflective surface,    -   wherein the another side of the movable plate has at least two        recesses, and the magnetic material is provided in the recesses.

According to a second aspect of the present invention, there is provideda method of producing an optical deflector having a supportingsubstrate, an elastic supporting part and a movable plate, comprisingthe steps of:

-   -   preparing a silicon substrate having a first side for formation        of a reflective surface and a second side;    -   forming mask layers on the first and the second sides of the        silicon substrate;    -   removing the mask layer on the first side except an area thereof        for formation of the supporting substrate, elastic supporting        part and movable plate;    -   removing the mask layer on the second side except an area        thereof for formation of the supporting substrate, elastic        supporting part and movable plate and also removing the mask        layer on an area for formation of a recess within the area for        formation of the movable plate;    -   dipping the silicon substrate in an aqueous alkaline solution to        perform anisotropic etching to divide the silicon substrate into        the supporting substrate, the elastic supporting part and the        movable plate and to form the recess on one side of the movable        plate;    -   removing the mask layers on the silicon substrate;    -   forming a reflective film on the first side of the movable        plate; and    -   providing a magnetic material in the recess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an optical deflector according to afirst embodiment of the invention;

FIG. 2 is a cross-sectional view taken along the line 2—2 in FIG. 1;

FIG. 3 is a perspective view illustrating a supporting substrate, amovable plate, an elastic supporting part, a recess and a permanentmagnet of FIG. 1;

FIG. 4 is a perspective view of an optical deflector according to asecond embodiment of the invention;

FIGS. 5A, 5B and 5C are cross-sectional views taken along the lines5A—5A, 5B—5B and 5C13 5C in FIG. 4, respectively;

FIG. 6 is a perspective view of an optical deflector according to athird embodiment of the invention;

FIG. 7 is a cross-sectional view taken along the line 7—7 in FIG. 6;

FIG. 8 is a perspective view of an optical deflector according to afourth embodiment of the invention;

FIG. 9 is a cross-sectional view taken along the line 9—9 in FIG. 8;

FIG. 10 is a perspective view of an optical deflector according to afifth embodiment of the invention;

FIG. 11 is a cross-sectional view taken along the line 11—11 in FIG. 10;

FIGS. 12A, 12B, 12C, 12D, and 12E are views illustrating a method ofproducing the optical deflector shown in FIG. 4;

FIGS. 13A, 13B, 13C, 13D, 13E, and 13F are views illustrating a methodof producing the optical deflector shown in FIG. 10;

FIG. 14 is a view showing an embodiment of an optical device using anoptical deflector of the invention;

FIG. 15 is a view showing another embodiment of an optical device usingan optical deflector of the invention;

FIG. 16 is a view showing a first conventional optical deflector; and

FIG. 17A is an exploded perspective view of a second conventionaloptical deflector, and FIG. 17B is a schematic, longitudinal sectionalview of the optical deflector of FIG. 17A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of the invention will bedescribed in detail with reference to the drawings.

(First Embodiment)

(Entire Configuration and Mirror (Movable Plate))

FIG. 1 is a perspective view showing a configuration of an opticaldeflector according to a first embodiment of the invention. In FIG. 1,an optical deflector 1 comprises a supporting substrate 2, a movableplate 6, and elastic supporting parts 3, the movable plate 6 beingsupported at both ends thereof on the supporting substrate 2 via theelastic supporting parts 3. The elastic supporting parts 3 support themovable plate 6 in such a manner that the movable plate 6 can beelastically and torsionally vibrated about a C axis (that is, a torsionaxis) in a direction indicated by the arrow E. One surface of themovable plate 6 is a reflective surface 4 that constitutes a mirrorsurface, and torsional movement of the movable plate 6 in the Edirection provides deflection of a light incident on the reflectivesurface 4 at a predetermined angle. The direction indicated by the arrowB in FIG. 1 is perpendicular to the torsion axis C and parallel to aplane in which the reflective surface 4 of the movable plate 6 isformed. The direction indicated by the arrow B is referred to as“movable plate width direction”.

(Magnet and Recess)

In a surface of the movable plate 6 opposite to the reflective surface 4(hereinafter, referred to as “back surface”), a plurality of recesses 5is formed parallel to the B direction. This back surface refers to asurface of the movable plate 6 opposite to the reflective surface 4,that is, a surface having no reflective surface formed thereon. Inparticular, in two of the plurality of recesses 5, permanent magnets 7,for example rare-earth permanent magnets containingsamarium-iron-nitrogen, are embedded. The permanent magnets 7 are eachmagnetized to opposite polarities with the torsion axis C therebetween.

(Integral Formation and Mirror Substrate)

The supporting substrate 2, the movable plate 6, the reflective surface4, the elastic supporting parts 3, and the recesses 5 as described laterare integrally formed from single-crystal silicon by a micromachiningtechnique, which is an application of the semiconductor producingtechnology.

(Description of Coil Substrate)

A coil substrate 8 is disposed parallel to the supporting substrate 2 insuch a manner that a coil 9 serving as a magnetism generating means isplaced in the vicinity of the permanent magnets 7 and at a desireddistance therefrom. The coil 9 is formed integrally on a surface of thecoil substrate 8 by, for example, electro-plating of copper in aconvolute shape. The magnetism generating means and the magnets servestogether as a driving means to drive the movable plate and thesupporting substrate relative to each other. Specifically, the movableplate can torsionally be vibrated with respect to the supportingsubstrate.

(Action)

Referring to FIG. 2, an action of the optical deflector 1 according tothis embodiment will be described. FIG. 2 is a cross-sectional view ofthe optical deflector 1 shown in FIG. 1, taken along the line 2—2 inFIG. 1. As shown in FIG. 2, the permanent magnet 7 is magnetized toopposite polarities on both sides of the torsion axis C, and thedirection of magnetization is as shown in the figure, for example. Whenthe coil 9 is energized, a magnetic flux Φ is produced in a direction,for example as shown in FIG. 2, depending on the direction of theapplied current. At the magnetic poles of the permanent magnet 7,attractive force and repulsive force are generated, respectively, inrelation to the direction of the magnetic flux, and a torque T isapplied to the movable plate 6, which is elastically supported aroundthe torsion axis C. Similarly, if the current is applied to the coil 9in the opposite direction, the torque T is applied thereto in theopposite direction. Therefore, as shown in FIG. 2, the movable plate 6can be driven to any angle depending on the current applied to the coil9.

(Resonance)

Furthermore, if an alternating current is applied to the coil 9, themovable plate 6 can be torsionally vibrated continuously. In this case,if the frequency of the alternating current is made substantiallycoincide with the resonance frequency of the movable plate 6 to make themovable plate 6 resonate, a larger angle displacement can be provided.

(Scale)

For example, the optical deflector 1 of this embodiment is driven at afrequency of 19 kHz, which is a resonance frequency of the movable plate6, and with a mechanical angle displacement of ±10°. The supportingsubstrate 2, the movable plate 6 and the elastic supporting parts 3 allhave an equal thickness of 150 μm. The movable plate 6 has a width inthe B direction of 1.3 mm and a length in the direction of torsion axisof 1.1 mm. Each of the elastic supporting parts 3 has a length of 2700μm and a width of 68 μm. That is, the area of the surface of the movableplate is on the order of several mm² (in particular, 2 mm² or less), andthus, the supporting substrate with the movable plate is amicrostructure.

(Detailed Description of Configuration of Movable Plate)

Here, FIG. 3 is a perspective view of the supporting substrate 2, viewedfrom the backside thereof.

As shown in FIG. 3, in this embodiment, a plurality of recesses 5parallel to the B direction are formed in the back surface of themovable plate 6. In particular, in two of the plurality of recesses 5,permanent magnets 7 are embedded parallel to the B direction.

Thus, according to this embodiment, the movable plate 6 is reduced inweight and the moment of inertia about the torsion axis C is alsoreduced, as compared to the case where the movable plate is a simplerectangular-parallelepiped member without any recess. In particular, themoment of inertia of the movable plate 6 is determined by the total sumof the products of the masses of the fractional parts of the movableplate 6 and the squares of the distances of the respective parts fromthe torsion axis C. Therefore, provision of the recesses 5 in themovable plate 6 as shown in FIG. 3, which results in less of a weight ofsilicon at an increasing distance from the torsion axis C, caneffectively reduce the moment of inertia thereof.

On the other hand, as shown in FIG. 3, the plurality of recesses 5formed in the movable plate 6 are arranged along the torsion axis C inrows (the direction of each of the recesses is perpendicular to thetorsion axis C), and solid parts between the rows allow the movableplate 6 to be effectively supported. Thus, in the optical deflector 1according to this embodiment, the moment of inertia of the movable plate6 can be effectively reduced while maintaining a sufficient rigiditythereof. In addition, no recess 5 is provided near the torsion axis C(in other words, no recess is provided at the center of the movableplate 6, or there is no recess extending over the torsion axis C). As aresult, more solid parts are provided near the torsion axis C. When themovable plate 6 is torsionally vibrated, a larger bending moment isloaded on a part nearer to the torsion axis C. Therefore, arrangement ofthe recesses 5 as shown in FIG. 3 can provide a minimum loss of rigidityof the mirror (or rigidity of the movable plate).

(Description of Shape of Magnet)

The permanent magnets 7 of this embodiment are embedded in the recesses5 formed in the movable plate 6. In the figure, two of the plurality ofrecesses are provided extending over the torsion axis C, and these tworecesses have permanent magnets embedded therein. The two recesseshaving the permanent magnets provided therein are disposed at positionsnearest the respective elastic supporting parts 3. By embedding thepermanent magnets 7 in the recesses 5 formed in the movable plate 6, anadditional rigidity can effectively be provided to the movable plate 6,which has been reduced in rigidity because of provision of the recesses5. In particular, the recesses 5 formed are parallel to the B directionand in an elongated shape, and the permanent magnets 7 provided thereinhave a similar shape. In this case, the rigidity of the movable plate 6(or rigidity of the mirror) can be increased without significantlyincreasing the moment of inertia of the movable plate 6.

Furthermore, if the permanent magnet 7 is made of a material having ahigher Young's modulus than the material of the movable plate 6(single-crystal silicon in the case of the optical deflector 1 of thisembodiment), the movable plate 6 can have a higher rigidity than in thecase where the movable plate is a simple rectangular-parallelepipedmember without any recess 5.

Furthermore, according to this embodiment, when compared to a case wherethe permanent magnet 7 is placed on the surface of the movable plate 6,the permanent magnet 7 can be placed close to the torsion axis C, andthus, the moment of inertia of the movable plate 6 can be reduced.

In addition, since the center of gravity of the movable plate 6 is alsolocated closer to the torsion axis C, stable torsional vibration withless undesirable fluctuations can be attained.

(Shape of Magnet)

In addition, such a shape of the permanent magnet 7 of the opticaldeflector 1 according to this embodiment is advantageous also in termsof torque generation. In other words, the shape of the permanent magnethas a good effect on torque generation. In order to generate a largetorque, it is desirable that the permanent magnet 7 provided in themovable plate 6 has as high a residual flux density as possible. Asgenerally known, magnets are subject to self-demagnetization dependingon their shapes, and therefore, for example, a cylindrical magnet havinga larger ratio L/D between the diameter D and the length L (having ashape with a larger permeance coefficient) has a lower selfdemagnetization and, thus, a higher residual flux density. The permanentmagnet 7 of the invention, which is embedded in the elongated recess 5parallel to the B direction and thus has a low self-demagnetization anda high residual flux density, can provide an actuator capable ofgenerating a large torque.

In FIG. 1, the reflective surface 4 serves as an optical deflectorelement. However, if the reflective surface 4 is replaced with areflective diffraction grating, an optical deflector that is operated inthe same manner by torsional vibration of the movable plate 6 can beprovided. In this case, deflection of the incident light providesdiffracted light. Therefore, a plurality of deflected light beams can bederived from one incident light beam. In the embodiments describedbelow, description will be made for the case where the reflectivesurface 4 is used as the optical deflector element. However, in all theembodiments described below, the reflective surface 4 can be replacedwith the reflective diffraction grating.

(Second Embodiment)

FIG. 4 is a perspective view of an optical deflector according to asecond embodiment of the invention. An optical deflector 21 of thisembodiment is essentially the same in driving principle as the opticaldeflector 1 of the first embodiment. Furthermore, as in the firstembodiment, the optical deflector 21 is integrally formed fromsingle-crystal silicon by a micromachining technique, which is anapplication of the semiconductor producing technology.

The difference between FIG. 4 and FIG. 1 is the configuration of thesupporting substrate 2, the elastic supporting parts 3, the movableplate 6, the recess 5, and the permanent magnet 7. These differenceswill be described in the following section. Here, in FIG. 4, partsidentical to those in FIG. 1 are assigned the same reference numerals.

FIG. 5A is a cross-sectional view taken along the line 5A—5A in FIG. 4,FIG. 5B is a cross-sectional view taken along the line 5B—5B in FIG. 4,and FIG. 5C is a cross-sectional view taken along the line 5C—5C in FIG.4. The respective surfaces of the elastics supporting parts 3 and therecess are constituted by (111)-equivalent planes of single-crystalsilicon, as shown in FIGS. 5A and 5B. The recess is provided so as notto extend over the torsion axis. Here, for example, a (−1-11) plane, a(11-1) plane and the like are collectively referred to as(111)-equivalent plane, and a (−100) plane and the like are collectivelyreferred to as (100)-equivalent plane. The (100)-equivalent plane andthe (111)-equivalent plane of silicon form an angle of about 54.7° witheach other, as shown in FIG. 5A. Therefore, as can be seen from FIG. 5A,the side and back surfaces of the movable plate 6 can be constituted bythe (111)-equivalent planes in a concave shape. As can be seen from FIG.5C, the cross section of the elastic supporting part 3 taken along theline 5C—5C is in the shape of the letter X formed by the (111)- and(100)-equivalent planes.

As can be seen from FIG. 5B, the recess 5 formed in the back surface ofthe movable plate 6 has a cross section, taken along the line 5B—5B, inthe shape of the letter V formed by the (111)-equivalent planes. Asshown in FIGS. 4 and 5B, permanent magnets 7, which are formed from aniron-cobalt-chromium alloy wire, for example, have a cylindrical shapeand are fitted into two of the recesses 5 and bonded thereto.

The recesses 5 and the permanent magnet 7 of this embodiment have thesame effect as the recesses 5 and the permanent magnet 7 of the opticaldeflector 1 of the first embodiment. Furthermore, in the opticaldeflector 21 of this embodiment, since the movable plate 6 also has theconcave shapes formed by the (111)-equivalent planes in its side wall,the moment of inertia of the movable plate 6 can be effectively reduced.In addition, since the permanent magnets 7 are in the shape of anelongated cylinder, self-demagnetization can be effectively reduced.

In the optical deflector 21 of this embodiment, the permanent magnet 7having a circular cross section is fitted into the recess 5 having aV-shaped cross section. In particular, in the direction of the torsionaxis C, the permanent magnet is secured by the (111)-equivalent planesof the recess 5 and can be positioned with a higher accuracy. Owing tothis, variations among products in characteristics of the opticaldeflector, such as generated torque or resonance frequency, can bereduced.

In addition, since the cross section of the elastic supporting part 3 isin the shape of an X-shaped polygon formed by the (100)- and(111)-equivalent planes of silicon, the movable plate 6 can beelastically supported with torsional rotation thereof about the torsionaxis C being facilitated and displacement in directions perpendicular tothe torsion axis C being reduced. Due to the elastic supporting part 3having such an X-shaped cross section, fluctuations of the movable plate6 other than the torsional vibration about the torsion axis C areprevented from occurring, and an optical deflector with less disturbancecan be provided.

(Method of Production)

Now, a method of producing the supporting substrate 2, the elasticsupporting part 3, the movable plate 6 and the recess 5 will bedescribed with reference to FIGS. 12A to 12E. FIGS. 12A to 12E showsteps of the method of producing the supporting substrate 2, the elasticsupporting part 3, the movable plate 6 and the recess 5 by anisotropicetching using an aqueous alkaline solution according to this embodiment.These drawings show schematic cross sections thereof taken along theline 5A—5A in FIG. 4 in the respective steps. First, as shown in FIG.12A, silicon-nitride mask layers 101 are formed on both surfaces of aplanar silicon substrate 104 by low pressure chemical vapor depositionor the like.

Then, as shown in FIG. 12B, the mask layer 101 on the surface on whichthe reflective surface 4 is to be formed is patterned in accordance withcontours of the supporting substrate 2, the movable plate 6 and theelastic supporting part 3 to be formed. This patterning is conducted bynormal photolithography and dry etching using a gas having an erosiveaction on silicon nitride (CF₄, for example). In addition, as shown inFIG. 12C, the mask layer 101 on the surface on which no reflectivesurface 4 is to be formed is patterned in accordance with contours ofthe supporting substrate 2, the movable plate 6, the elastic supportingpart 3 and the recess 5 to be formed. This patterning is conducted inthe same manner as that shown in FIG. 12B.

Then, as shown in FIG. 12D, anisotropic etching is performed by dippingthe substrate for a desired time in an aqueous alkaline solution havingsignificantly different erosion rates for crystal faces ofsingle-crystal silicon (for example, an aqueous potassium hydroxidesolution, an aqueous tetramethylammonium hydroxide solution, etc.),thereby forming the supporting substrate 2, the movable plate 6, theelastic supporting part 3 and the recess 5 which are shaped as shown inFIG. 12D. In the anisotropic etching, the etch rate is greater for the(100)-equivalent plane and smaller for the (111)-equivalent plane.Therefore, the silicon substrate 104 is etched from the front and backsurfaces thereof, and due to the relation of the patterns of the masklayers 101 with the silicon crystal faces, the silicon substrate 104 canbe precisely etched into a shape formed by the (100)-equivalent planescovered with the mask layers 101 and the (111)-equivalent planes. Thatis, by this alkaline anisotropic etching, the recess 5 constituted bythe (111)-equivalent planes is formed in the back surface of the movableplate 6, and the concave shape constituted by the (111)-equivalentplanes is formed in the side faces thereof. At the same time, in thisetching step, the elastic supporting parts 3 are also worked in the formof an X-shaped polygon formed by the (100)- and (111)-equivalent planes(see FIG. 5C).

Then, as shown in FIG. 12E, the silicon nitride mask layers 101 areremoved, and a metal having a high reflectivity (for example, aluminum)is vacuum-evaporated as the reflective surface 4. In this way, thesupporting substrate 2, the movable plate 6 with the recesses 5, thereflective surface 4 and the elastic supporting parts 3 are integrallyformed.

Finally, a wire of metal magnet (for example, an iron-cobalt-chromiumalloy) that is easy to process is cut into a desired length and bondedinto the recess 5 by an adhesive or the like. Then, the metal magneticwire is magnetized to provide the permanent magnet 7 (as for thedirection of magnetization, see FIG. 2). In this way, the opticaldeflector 21 shown in FIG. 4 is completed.

As described above, according to the method of producing the opticaldeflector 21 of this embodiment, both the movable plate 6 and theelastic supporting parts 3 can be formed in a single alkalineanisotropic etching process, and thus, mass production at an extremelylow cost can be attained. In addition, since changes in design or thelike can be provided for by adjusting the lithographic mask pattern andthe etching time, the optical deflector can be produced at a lower costand with a short development period. In addition, since the shapes ofthe movable plate 6 and the elastic supporting parts 3 are determined bythe (111)-equivalent planes of single-crystal silicon, they can beprocessed with a higher precision.

In addition, since the permanent magnet 7 is formed by cutting a wirehaving a circular cross section, the optical deflector can be producedat a lower cost and with a higher processing precision.

(Third Embodiment)

FIG. 6 is a perspective view of an optical deflector according to athird embodiment of the invention.

An optical deflector 31 according to this embodiment has the supportingsubstrate 2 and the elastic supporting parts 3 similar to those of theoptical deflector 21 of the second embodiment, which have the sameeffect as those of the optical deflector 21. Furthermore, as in thesecond embodiment, the optical deflector 31 is integrally formed fromsingle-crystal silicon by a micromachining technique, which is anapplication of the semiconductor producing technology.

The difference of FIG. 6 from FIG. 4 is the configuration of the recess5 and the permanent magnet 7, and these will be described in particularin the following. Here, in FIG. 6, parts identical to those in FIG. 4are assigned the same reference numerals.

FIG. 7 is a cross-sectional view taken along the line 7—7 in FIG. 6. Theinner surfaces of the recess 5 are constituted by (111)-equivalentplanes of single-crystal silicon wafer as with the optical deflector 21of the second embodiment, and as shown in FIG. 7, the cross section ofthe recess 5 taken along the line 7—7 is in the shape of the letter V.In particular, in the optical deflector 31 of this embodiment, all therecesses 5 formed in the movable plate 6 are arranged symmetrically withrespect to the torsion axis C, and no recess 5 is formed in the vicinityof the torsion axis C.

All the recesses 5 formed in the movable plate 6 have the respectivepermanent magnets 7 embedded therein.

The recesses 5 and the permanent magnets 7 in this embodiment have thesame effects as the recesses 5 and the permanent magnets 7 of theoptical deflector 1 of the first embodiment. However, in the opticaldeflector 31 of this embodiment, since no recess 5 is formed in thevicinity of the torsion axis C, rigidity of the movable plate 6 due toformation of the recesses 5 can be further reduces. In addition, sinceall the recesses are filled with the permanent magnets 7, even if themovable plate 6 is thin and the recesses 5 can have only an insufficientdepth, the magnet can be used in an increased amount and a highgenerating power can be obtained.

(Method of Production)

When producing the optical deflector according to this embodiment, themethod of production shown in FIGS. 12A to 12E can be used. However, inthe step shown in FIG. 12C, the pattern of the mask layer 101corresponding to the recesses 5 is changed to that as shown in FIG. 6.Then, by sequentially conducting the steps shown in FIGS. 12D and 12E,the supporting substrate 2, the movable plate 6, the elastic supportingparts 3 and the recesses 5 are formed as shown in FIG. 6. Then, thepermanent magnets 7 are electro-plated with an alloy containingnickel-cobalt-phosphor, for example, polished and embedded in all therecesses 5. Finally, magnetization is performed (as for the direction ofmagnetization, see FIG. 2) to provide the permanent magnets 7, and thus,the optical deflector 31 shown in FIG. 6 is completed.

(Fourth Embodiment)

FIG. 8 is a perspective view of an optical deflector according to afourth embodiment of the invention.

An optical deflector 41 according to this embodiment has the supportingsubstrate 2 and the elastic supporting parts 3 similar to those of theoptical deflector 21 of the second embodiment, which have the sameeffect as those of the optical deflector 21. Furthermore, as in thesecond embodiment, the optical deflector 41 is integrally formed fromsingle-crystal silicon by a micromachining technique, which is anapplication of the semiconductor producing technology.

The difference of FIG. 8 from FIG. 4 is the configuration of the recess5 and the permanent magnet 7, and this will be described in particularin the following. Here, in FIG. 8, parts identical to those in FIG. 4are assigned the same reference numerals.

FIG. 9 is a cross-sectional view taken along the line 9—9 in FIG. 8. Theinner surfaces of the recess 5 are constituted by (111)-equivalentplanes of single-crystal silicon wafer as with the optical deflector 21of the second embodiment, and as shown in FIG. 9, the cross section ofthe recess 5 taken along the line 9—9 is in the shape of the letter V.In particular, in the optical deflector 41 of this embodiment, thepermanent magnet 7 is in the form of a planar rectangular parallelepipedand provided above the recess 5 as shown in FIG. 9.

The recesses 5 and the permanent magnets 7 in this embodiment have thesame effects as the recesses 5 and the permanent magnets 7 of theoptical deflector 1 of the first embodiment.

However, in the optical deflector 41 of this embodiment, the permanentmagnet 7 covers tops of the recess 5 to provide a hollow. Thus, therigidity of the movable plate 6 reduced by formation of the recesses 5can be effectively compensated for with less of an amount of permanentmagnet 7.

(Method of Production)

When producing the optical deflector according to this embodiment, themethod of production shown in FIGS. 12A to 12E can be used. Bysequentially conducting the steps shown in FIGS. 12A to 12E, thesupporting substrate 2, the movable plate 6, the elastic supportingparts 3 and the recesses 5 are formed as shown in FIG. 8.

Then, a sheet of metal magnet (for example, an iron-cobalt-chromiumalloy) which is easy to process is cut into desired width and length toform a rectangular parallelepiped, which is then bonded over the recess5 by an adhesive or the like. Finally, magnetization is performed (asfor the direction of magnetization, see FIG. 2) to provide the permanentmagnets 7. Thus, the optical deflector 41 shown in FIG. 8 is completed.

(Fifth Embodiment)

FIG. 10 is a perspective view of an optical deflector according to afifth embodiment of the invention.

An optical deflector 51 according to this embodiment has the supportingsubstrate 2 and the elastic supporting parts 3 similar to those of theoptical deflector 21 of the second embodiment, which have the sameeffect as those of the optical deflector 21. Furthermore, as in thesecond embodiment, the optical deflector 51 is integrally formed fromsingle-crystal silicon by a micromachining technique, which is anapplication of the semiconductor producing technology.

The difference of FIG. 10 from FIG. 4 is the configuration of the recess5 and the permanent magnet 7, and this will be described in particularin the following. Here, in FIG. 10, parts identical to those in FIG. 4are assigned the same reference numerals.

FIG. 11 is a cross-sectional view taken along the line 11—11 in FIG. 10.The inner surfaces of the recess 5 are constituted by (111)-equivalentplanes of single-crystal silicon wafer as with the optical deflector 21of the second embodiment, and as shown in FIG. 11, the cross section,taken along the line 11—11, of a recess 5 in which the permanent magnet7 is to be provided is in the shape of a rhombus, and the cross sectionof the other recesses 5 is in the shape of the letter V. In particular,in the optical deflector 51 of this embodiment, the permanent magnet 7is embedded in the recess 5 having a rhombic cross section.

The recesses 5 and the permanent magnets 7 in this embodiment have thesame effects as the recesses 5 and the permanent magnets 7 of theoptical deflector 1 of the first embodiment.

However, in the optical deflector 51 of this embodiment, as shown inFIG. 11, the recess 5 in which the permanent magnet 7 is embedded has arhombic cross section. Therefore, even if adhesion between the permanentmagnet 7 and the movable plate 6 is poor or even if the internal stressis high, the possibility that the permanent magnet 7 peels off from themovable plate 6 can be reduced.

(Method of Production)

Now, a method of producing the supporting substrate 2, the elasticsupporting part 3, the movable plate 6 and the recess 5 will bedescribed with reference to FIGS. 13A to 13F. FIGS. 13A to 13F showssteps in the method of producing the supporting substrate 2, the elasticsupporting part 3, the movable plate 6 and the recess 5 by etchingaccording to this embodiment. These drawings show schematic crosssections thereof taken along the line 11—11 in FIG. 10 in the respectivesteps. First, as shown in FIG. 13A, silicon-nitride mask layers 101 areformed on both surface of a planar silicon substrate 104 by low pressurechemical vapor deposition or the like.

Then, as shown in FIG. 13B, the mask layer 101 on the surface on whichthe reflective surface 4 is to be formed is patterned in accordance withcontours of the supporting substrate 2, the movable plate 6 and theelastic supporting part 3 to be formed. This patterning is conducted bynormal photolithography and dry etching using a gas having an erosiveaction on silicon nitride (CF₄, for example).

Then, as shown in FIG. 13C, the mask layer 101 on the surface oppositeto the surface on which the reflective surface 4 is to be formed ispatterned in accordance with the contour of a recess 5 in which thepermanent magnet 7 is to be provided. Then, dry etching of the siliconis conducted using an ICP-RIE (Inductively Coupled Plasma-Reactive IonEtching) device to form a groove 10.

Then, as shown in FIG. 13D, the mask layer 101 on the surface on whichno reflective surface 4 is to be formed is patterned in accordance withcontours of the supporting substrate 2, the movable plate 6, the elasticsupporting part 3 and the other recesses 5 to be formed.

Then, as shown in FIG. 13E, anisotropic etching is performed by dippingthe substrate for a desired time in an aqueous alkaline solution havingsignificantly different erosion rates for crystal faces ofsingle-crystal silicon (for example, an aqueous potassium hydroxidesolution, an aqueous tetramethylammonium hydroxide solution), therebyforming the supporting substrate 2, the movable plate 6, the elasticsupporting part 3 and the recess 5 which are shaped as shown in FIG.13E. In the anisotropic etching, the etching rate is greater for the(100)-equivalent plane and smaller for the (111)-equivalent plane.Therefore, the silicon substrate 104 is etched from the front and backsurfaces thereof, and due to the relation of the patterns of the masklayers 101 and the silicon crystal faces, the silicon substrate 104 canbe precisely etched into a shape formed by the (100)-equivalent planescovered with the mask layers 101 and the (111)-equivalent planes. Thatis, by this alkaline anisotropic etching, the recess 5 constituted bythe (111)-equivalent planes is formed in the back surface of the movableplate 6, and the concave shape constituted by the (111)-equivalentplanes is formed in the side faces thereof. At the same time, in thisetching step, the elastic supporting parts 3 is also provided in theform of an X-shaped polygon formed by the (100)- and (111)-equivalentplanes (see FIG. 5C). In particular, at the region where the groove 10is previously formed, a recess having a rhombic cross section isprovided.

Then, as shown in FIG. 13F, the silicon nitride mask layers 101 areremoved, and a metal having a high reflectivity (for example, aluminum)is vacuum-evaporated as the reflective surface 4. In this way, thesupporting substrate 2, the movable plate 6 with the recesses 5, thereflective surface 4 and the elastic supporting parts 3 are integrallyformed.

Then, a magnetic material in a paste form, which is a mixture ofrare-earth material powder containing samarium-iron-nitrogen and abonding material, is applied into the recess 5. Here, silk-screenprinting can be used to apply the magnetic material only to the recess 5having the rhombic cross section. Finally, after heat treatment in amagnetic field, magnetization is conducted to form the permanent magnet7 (as for the direction of magnetization, see FIG. 2). In this way, theoptical deflector 51 shown in FIG. 10 is completed.

(Sixth Embodiment)

FIG. 14 shows an embodiment of an optical device using any one of theoptical deflectors described above. In this embodiment, an image displaydevice is adopted as the optical device. In FIG. 14, reference numeral201 denotes an optical deflector group having two optical deflectorsaccording to any one of the first to the fifth embodiments disposed withthe deflection directions being perpendicular to each other. In thisembodiment, the optical deflector group is used as an optical scannerdevice for raster-scanning an incident light in the horizontal andvertical directions. Reference numeral 202 denotes a laser source,reference numeral 203 denotes a lens or lens group, reference numeral204 denotes a writing lens or writing lens group, and reference numeral205 denotes a projection plane. An incident laser beam from the lasersource 202 is subject to a predetermined intensity modulation associatedwith a scan timing and scans two-dimensionally under the action of theoptical deflector group 201. The scanning laser beam forms an image onthe projection plane 205 by means of writing lens 204. In short, theimage display device according to this embodiment can be applied todisplay products.

(Seventh Embodiment)

FIG. 15 shows another embodiment of an optical device using any one ofthe optical deflectors described above. In this embodiment, anelectrophotographic image forming device is adopted as the opticaldevice. In FIG. 15, reference numeral 201 denotes an optical deflectoraccording to any one of the first to the fifth embodiments, which is, inthis embodiment, used as an optical scanner device for scanning anincident light one-dimensionally. Reference numeral 202 denotes a lasersource. Reference numeral 203 denotes a lens or lens group, referencenumeral 204 denotes a writing lens or writing lens group, and referencenumeral 206 denotes a photosensitive body. A laser beam emitted from thelaser source is subject to a predetermined intensity modulationassociated with a scan timing and scans one-dimensionally under theaction of the optical deflector 201. The scanning laser beam forms animage on the photosensitive body 206 by means of the writing lens 204.

The photosensitive body 206 is previously electrically charged uniformlyby a charger (not shown), and the photosensitive body is scanned with alight beam to form an electrostatic latent image at the scanned area.Then, a developing device (not shown) develops the electrostatic latentimage to form a toner image. Then, the toner image is transferred andfixed to a sheet of paper (not shown), for example, whereby the image isformed on the sheet of paper.

As described above referring to the embodiments, according to theoptical deflector according to the present invention, since a recess isformed in a surface of a movable plate opposite to a reflective surfacethereof, the moment of inertia of the movable plate can be reduced whileassuring a high rigidity, and since a magnetic material is provided inthe recess, the rigidity of the movable plate can be further increased.Furthermore, when compared to the case where a magnetic material isdisposed on a surface of a movable plate, the magnetic material can bedisposed close to a torsion axis, so that the moment of inertia of themovable plate 6 can be reduced.

Therefore, there can be realized a small optical deflector that can bedriven at a high speed and provide a large angle of deflection with lesspower consumption and shows less deformation of a reflective surfaceeven in high-speed operation.

1. An optical deflector, comprising: a supporting substrate having anelastic supporting part; a movable plate having a reflective surface onone side thereof and a magnetic material on another side thereof andsupported at both ends thereof by the elastic supporting part so as tobe torsionally vibratable around a torsion axis; and magnetismgenerating means provided in the vicinity of and spaced apart from themagnetic material, for driving the movable plate relative to thesupporting substrate to deflect light incident on the reflectivesurface, wherein the another side of the movable plate has at least tworecesses, and the magnetic material is provided in the recesses.
 2. Theoptical deflector according to claim 1, wherein the recesses are spacedapart from the torsion axis of the movable plate and are not close tothe torsion axis.
 3. The optical deflector according to claim 1, whereinthe supporting substrate, the elastic supporting part, the movableplate, and the recesses are integrally formed of single-crystal silicon.4. The optical deflector according to claim 1, wherein the first side ofthe movable plate comprises a (100)-equivalent plane of a siliconcrystal, and an inner surface of at least one of the recesses comprisesa (111)-equivalent plane of a silicon crystal.
 5. The optical deflectoraccording to claim 1, wherein the elastic supporting part has anX-shaped cross section.
 6. The optical deflector according to claim 1,wherein a side wall of the movable plate has a recess.
 7. The opticaldeflector according to claim 1, wherein the recesses each have asubstantially vertical side wall in a cross section taken along a lineperpendicular to the direction of a width of the movable plate.
 8. Theoptical deflector according to claim 1, wherein the recesses are eachsubstantially V-shaped in a cross section taken along a lineperpendicular to the direction of a width of the movable plate.
 9. Theoptical deflector according to claim 1, wherein a cross section of eachof the recesses which is parallel to the second side of the movableplate has a larger area within the movable plate than at a surface ofthe movable plate.
 10. The optical deflector according to claim 1,wherein the magnetic material has a substantially circular cross sectiontaken along a line perpendicular to the direction of a width of themovable plate.
 11. The optical deflector according to claim 1, wherein,when viewed from above the surface of the movable plate having therecesses formed therein, the magnetic material overlies the recesses.12. An optical device, comprising the optical deflector as set forth inclaim
 1. 13. A display device comprising the optical deflector as setforth in claim 1 and a light source, wherein the optical deflectorperforms deflection/scanning of light from the light source to form animage on a projection plane.